Extreme pressure lubricant additive



United States Pate.

dice

Patented Sept. 26, 1961 This invention relates to lubricating oil compositions having a high load-carrying ability. Particularly, the invention relates to hypoid gear lubricants comprising lubricating oil, a sulfur and chlorine containing paraffinic material and a metal dialkyl dithiophosphate.

Paraffinic materials substituted with both sulfur and chlorine, as well as zinc dialkyl dithiophosphates are known as lubricating oil additives. However, it has now been found that when used together in certain proportions, the combination results in greatly enhanced loadcarrying ability and decreased wear than would be ex pected from the additive efiect of each component. Specifically, it has been found that outstanding gear lubricants may be prepared, which comprise a mineral lubricating oil base obtained from a parafliuic, naphthenic or mixed base crude, about 1 to 20, e.g. 3 to 12, weight percent of a sulfur and chlorine containing paraflinic material and about 1 to 20, e.g. 3 to 12, weight percent of a zinc dialkyl dithiophosphate. Generally, a total of about 2 to wt. percent of the combined additives will be used.

The zinc dialkyl dithiophosphates used in the present invention are those wherein each alkyl group contains 3 to 20, preferably 6 to 15 carbon atoms and may be either branched or straight chain. Examples of such materials include zinc diisopropyl dithiophosphate, zinc dihexyl dithiophosphate, zinc dioctyl dithiophosphate, zinc dicapryl dithiophosphate and zinc dioctadecyl dithiophosphate. Several of the examples of the invention were carried out with a zinc dihexyl dithiophosphate wherein the hexyl groups are branched and were derived from methylisobutyl carbinol. phates and their preparation are well known in the art, e.g. see US. Patent 2,369,632.

The sulfur-chlorinated parafiinic materials which may be used in this invention will contain about 3 to 110, e.g. 4 to 8, weight percent of sulfur and about 10 to 40, e.g. to 35, weight percent of chlorine. Materials of this type may be prepared from aliphatic hydrocarbons having about 12 to 30 carbon atoms per molecule, for example, petroleum distillates such as kerosene, gas oils and lubricating oils, or from solid hydrocarbons such as parafiin wax or petrolatum. The additive may be pre pared in several Ways. 'For example, a suitable raw material such as panaifin wax or a liquid petroleum distillate such as kerosene, may be treated with a sulfur halide such as sulfur monoor dichloride in order to incorporate both sulfur and chlorine into the hydrocarbon material. A diiferent method, and one which is preferred commercially because it permits better technical control, is to chlorinate a suitable raw material such as parafiin wax, kerosene or naphtha to the desired chlorine control and then subsequently treat the resultant compound with sulfur or an inorganic sulfide such as sodium sulfide or polysulfide, or with sulfur and sodium hydroxide.

A specific example of the sulfur andchlorine containing material was prepared as follows: A chlorinated kerosene containing about 40% chlorine and a chlorinated wax containing about 33% chlorine are mixed together in a volume ratio of about 07:10 The mixture was then reacted with sodium hydrosulfide and elemental sulfur to form a product containing 30.0 weight percent chlorine and. .6 weight percent sulfur. This additive The above dithiophos-v was used in the working examples of the invention and is designated as Additive A.

The lubricating oil base of the composition is not critical, however, in formulating gear oils, it is preferred to use mineral lubricating oils having a viscosity index of about 40 to 130, and a viscosity at 210 F. of 60 to 300 SUS.

EXAMPLE I A lubricating oil composition was prepared by mixing 6.9 weight percent of Additive A (which is the sulfurchlorine containing material previously described), 5.5 weight percent of a zinc dihexyldithiophosphate (the hexyl groups were derived from methyl isobutyl carbinol) and 87.6 weight percent of a mineral lubricating oil having a V.I. of 90 and a viscosity at 100 F. of 1094 SUS (this base oil was used in all the examples of the invention). This composition was then tested for its load-carrying ability in a SAE machine operating at 1000 rpm. and a 14.6 shaft ratio and for wear properties.

The results of these tests are summarized in the following table along with tests made on the base oil per se and the base oil containing only the dithiophosphate or only the sulfur-chlorine additive:

As seen from Table I, the composition of the invention which contained both the dithiophosphate and sulfurchlorine additive had much greater load-carrying ability and gave less wear than either the sulfur-chlorinated material per se or the dithiophosphate material by itself.

EXAMPLE II Several more lubricating compositions were prepared similarly to that of Example I, except that varying amounts of the additives were used. The compositions of these lubricants and their load-carrying ability are summarized in Table II which follows:

Table II Composition Wt. Percent A B Additive A 7. 5 7.8 Zine dihexyl dithiophosphate 2. 0 4. 8 Mineral lubricating oil 91. 0 87. 4 Performance:

SAE Load-carrying test (lbs. carried) 315 450+ 3 shock cycles at 50 to 35 m.p.h., 60 to 45 m.p.h., and

70 to 55 m.p.h., respectively, followed by 10 more high speed cycles of 60 to 109 mph. The high speed cycles were carried out by rapidly accelerating from 60 to 109 m.p.h., then allowing the auto to coast until the speed was back to 60 m.p.h., then the cycle was repeated. The shock cycles were carried out by allowing the auto to coast from the higher speed until the lower speed was reached and then shifting into low gear. Upon completion of test the difierential was disassembled and the ring and pinion gears examined for scoring.

The CRC-L3-7-756 test was developed for the Ordnance Dept. and is titled Research Technique for Determining Load-Carrying, Wear, and- Extreme Pressure Characteristics of Universal Gear Lubricants in Axles Under Conditions of High-Speed, Low-Torque Operation, Followed by Low-Speed, High-Torque Operation. Briefly described this test is carried out as follows:

The test unit consists of a new ton army truck hypoid rear axle carrier, 5.83:1 ratio, installed in its own housing. The unit is driven by a six cylinder 235 cu. in. Chevrolet truck engine withstandard ignition and carburetor, with suitable transmission, couplings, and dynamometer parts.

Sequence 1 of the test consists of 100 minutes operation at a ring gear speed of 440: r.p.m. and a ring gear torque of 94601150 inch-lb. The gear oil temperature is 300 F. maximum.

Sequence 2 of the test consists of 24 hours operation at a ring gear speed of 8011 rpm. and a ring gear torque of 41,800i150 inch-lb. The oil temperature is 275 F.:3 F.

After completion of the above test, the ring and pinion gears are examined for evidence of surface distress and wear. The results of the above tests are shown in Table III, which follows. For comparison purposes, similar test data are shown for a commercial hypoid gear lubricant which contains a sulfur and chlorine containing additive but no dithiophosphate and a second lubricant which had been approved under military specification MIL 2105 for this use.

Table [11 FULL SCALE TESTS Lubricant Buick -A Test CRC-L-37-756 Pass-Few very light scratches on drive side of gear.

Pass-2% Light score on coast side of drive gear.

Fail-704.5% Medium heavy score on coast side of gear plus trace of wear.

Fail-100% Heavy score on coast and drive side of gear plus heavy wear.

Composition of Ex. I-

Commercial Hypoid Gear Lubricant.

Current MIL 2105 Approved Lubricant.

The results of Table III illustrate the striking superiority of the lubricants of the invention when tested in actual operation, when compared to other hypoid gear lubricants.

While the lubricants of'the invention may be formulated from zinc dialkyl dithiophosphates containing as low as 3 carbon atoms in each alkyl group, it is preferred that the alkyl groups contain above 6 carbon atoms, e.g. 6 to 15 carbon atoms in order to give the maximum rust protection. To illustrate this preference, several compositions of the invention were pepared and then tested for corrosion inhibiting characteristics as follows:

A sand-blasted steel panel was half immersed for 3 hours in an emulsion consisting of 2% wt. percent water in the lubricant while the emulsion was maintained. at 180 F. in a beaker in an oven. The panel was then removed, inverted in the beaker (i.e. placed with the coated half up) and the beaker was then placed on a tray in a closed desiccator maintained at 180 F. in an oven. The bottom of the desiccator contained a small amount of water. The temperature of the oven was then allowed to drop rapidly (30 minutes) to 135 F. so as to cause water condensation upon the surface of the panel. The panel was then maintained at 136 F. for 16 hours, then removed, cleaned with solvent and examined for rust.

Full scale rust tests were also carried out by operating a Spicer axle on the. lubicating oil composition-water emulsion for four hours at 180 F., followed by storage Table IV RUST RESISTANCE CHARACTERISTICS Composition Lab. Test Full Scale Test 5.2 wt. percent zinc dihexyl dithiophosphate 6.4 wt. percent Additive A. no rust No rust.

88.4 wt. percent Mineral lubricating oil 5.2 wt. percent zinc di-C dithrophosphete rust on area Rust and brown stains 6.4 wt. percent Additive A... exposed to on whole cover plate 88.4 wt. percent Mineral lubrimoist air. area.

eating oil As seen from the above table, the compositions prepared from the zinc dihexyl dithiophosphate (the hexyl groups were derived from methyl isobutyl carbinol) showed no rust, while the composition containing the dithiophosphate which had mixed alkyl groups of 4 and 5 carbon atoms each, did show rust. For this reason, it is preferred that the dithiophosphate have six or more carbon atoms in the alkyl group.

Other additive materials may also be added to the compositions of the invention to further improve its properties. For example, oxidation inhibitors, rust preventive agents, detergent additives, etc. may be added. To illustrate the use of other additive materials, the composition of Example I was mixed with 1.65 wt. percent of a commercially available barium salt of a hydrolyzed- P S treated olefin mixture. Upon storage for hours at 300 F., the amount of sediment formed was 0.93 wt. percent as compared to 2.7 wt. percent that was formed when no auxiliary additive was used.

in summary, this invention relates to an additive combination of a sulfur-and-chlorine containing paraffinic material and a zinc dialkyl dithiophosphate. This additive combination results in a higher load-carrying ability than would be expected from the individual load-carrying ability of either material by itself. This combination is particularly useful in formulating gear oils. When used in formulating gear oils for automotive transmission use, it has been found that about 6 to 12 wt. percent of the sulfur-and-chlorine containing additive and about 2 to 8 wt. percent of the zinc dialkyl dithiophosphate will give excellent results at economical concentrations, although. of course, for special applications it may be more desirable to use the additives in other concentrations and ratios as previously mentioned.

What is claimed is:

1. An improved hypoid gear lubricant having enhanced load-carrying, wear reducing and rust preventive properties which comprises a major portion of mineral lubricating oil having a viscosity at 210 F. in the range of 60 to 300 SUS and as the sole load-carrying additive a synergistic mixture consisting of: (A) 6 to 12 wt. percent of a sulfochlorinated product having 4 to 8 wt. percent sulfur and 20 to 35 wt. percent chlorine, said product being obtained by treating a blend of chlorinated kerosene and chlorinated wax with an inorganic sulfide and elemental sulfur, and 2 to 8 wt. percent of a zinc dialkyl dithiophosphate wherein each alkyl group contains 6 to 15 carbon atoms.

2. An improved hypoid gear lubricant according to claim 1, wherein said zinc dialkyl dithiophosphate is zinc dihexyl dithiophosphate and wherein said hexyl groups are derived from methyl isobutyl carbinol;

3. An improved hypoid gear lubricant according, to claim 1 wherein said load-carrying additive consists essentially of about 6.9 wt. percent of said sulfochlorinated 5 product and about 5.5 wt. percent of said zinc dialkyl 2,369,632 dithiophosphate having 6 carbon atoms per alkyl group. 2,514,625 2,850,452 References Cited in the file of this patent UNITED STATES PATENTS 5 752,571 2,364,284 Freuler Dec. 5, 1944 6 Cook et a1. Feb. 13, 1945 Clausen et a1. July 11, 1950 Sands et a1. Sept. 2, 1958 FOREIGN PATENTS Great Britain July 11, 1956 

1. AN IMPROVED HYPOID GEAR LUBRICANT HAVING ENHANCED LOAD-CARRYING, WEAR REDUCING AND RUST PREVENTIVE PROPERTIES WHICH COMPRISES A MAJOR PORTION OF MINERAL LUBRICATING OIL HAVING A VISCOSITY AT 210*F. IN THE RANGE OF 60 TO 300 SUS AND AS THE SOLE LOAD-CARRYING ADDITIVE A SYNERGISTIC MIXTURE CONSISTING OF: (A) 6 TO 12 WT. PERCENT OF A SULFOCHLORINATED PRODUCT HAVING 4 TO 8 WT. PERCENT SULFUR AND 20 TO 35 WT. PERCENT CHLORINE, SAID PRODUCT BEING OBTAINED BY TREATING A BLEND OF CHLORINATED KEROSENE AND CHLORINATED WAX WITH AN INORGANIC SULFIDE AND ELEMENTAL SULFUR, AND 2 TO 8 WT. PERCENT OF A ZINC DIALKYL DITHIOPHOSPHATE WHEREIN EACH ALKYL GROUP CONTAINS 6 TO 15 CARBON ATOMS. 